Whether a stay of federal proceedings under Colorado River Water Conservation District v. United States is permissible

QUESTION PRESENTED Whether a stay of federal proceedings under Colorado River Water Conservation District v. United States, 424 U.S. 800 (1976), is permissible only when a pending state court case will necessarily resolve the federal proceedings however it is decided (as the Ninth Circuit held below), or whether a stay is permissible when one of the potential outcomes in state court can completely resolve the case, even if a second potential outcome would leave further issues for federal litigation (as the Seventh Circuit has held).